How do i activate catalog help on my ti-84 + gc.

SOURCE: I have issues turning on my TI-Nspire using TI-84 Plus SE keypad

i would say use the normal key pad or send it in to T.I to fix.

SOURCE: Change TI 84 OS to TI 89 OS??

And why, pray tell, would you do such a thing? You will ruin your Ti84 Plus Silver Edition and will not have a working TI89. Besides, TI connect will refuse to transfer it.
If you like the capabilities of the TI89 Titanium, buy a cheap or used one on e-bay or amazon.com and spare your TI84PLus SE.

SOURCE: Finding the second derivative on a TI-84

nderiv(nderiv(sin(x),x,x),x,2)

SOURCE: I am using a TI-84 Plus graphical calculator. How do I use my GC (plysmlt2) to solve a derivative? eg. d/dx(x^6+x^4)=0

There is a command called nDeriv( which you find in the catalog. To open the catalog of commands press [SHIFT][0] (CATALOG), then scroll down or press N to jump to the 1st command starting with N.
Highlight the command then press ENTER. The command echoes on the main screen. Type in the function you want to differentiate, type in a comma to separate, type the name of the vatriable (X), then type in the value at which the derivative is to be evaluated. Close the right parenthesis, then press ENTER.
This is what you see with the newer OS that has MathPrint



With the newer OS with MODE set to Classic, here is what you see.


Hope it helps.